14 lines
269 B
Text
14 lines
269 B
Text
import data.nat.basic
|
||
open nat
|
||
|
||
theorem zero_left (n : ℕ) : 0 + n = n :=
|
||
nat.induction_on n
|
||
!add_zero
|
||
(take m IH,
|
||
begin
|
||
refine
|
||
(calc
|
||
0 + succ m = succ (0 + m) : _
|
||
... = succ m : IH),
|
||
esimp
|
||
end)
|